Operational Amplifier as the Summing Amplifier

In this post I will discuss about the Operational Amplifier configuration as the Summing Amplifier. In the last post I have discussed the Operational Amplifier as the Programmable Gain Amplifier. I have mentioned there that the Operational Amplifier can employ to perform a variety of operations and the Operation that each op-amp configuration performs is determined by the feedback network of the Operational Amplifier. For those who do not remember that the Operational Amplifier is always used in the feedback configuration and the feedback network can be purely resistive as the case for the Inverting and Non-Inverting Operational Amplifier configurations or it is a combination of the capacitors, inductors etc. in short the operation of the Operational Amplifier configuration is designed keeping in mind the feedback network. The point I am trying here to make is as most of you must have figured out that the Summing Amplifier as we will see in this post must have a unique feedback network and this feedback network of the summing amplifier must be properly designed to achieve the proper operation of the Summing Amplifier. Similarly the Operational Amplifier as Differential Amplifier, Instrumentation Amplifier all have unique feedback network for the typical task that each configuration performs.
After reading this post you will learn about the Operational Amplifier, Operational Amplifier as the Summing Amplifier, designing of the Operational Amplifier feedback network. So sit back, keep reading and enjoy learning.

Summing Amplifier:

Before diving deep into the discussion on the Operational Amplifier as the Summing amplifier let us understand what basically is the Summing Amplifier. As the name implies the Summing Amplifier is the type of Amplifier in which the signals applied at the input terminal are added and the sum of the input voltage signals appear at the Output terminal of the Amplifier. So it can be noticed that the Summing Amplifier is the single ended input and single ended output amplifier unlikely to the Differential Amplifier which is the Differential signal input and single ended output. The discussion on the single ended signaling and the differential Signaling is made in the previous post. The Summing Amplifier can be implemented in either Inverting configuration or Non-Inverting configuration. What I mean is that either the signals that are to be added are applied at the Inverting Input terminal or at Non-Inverting input terminal of the Operational Amplifier and either configuration will result in respective feedback network. The discussion on the feedback network of the Operational Amplifier as the Summing Amplifier will be made in the following sections.

Operational Amplifier as the Summing Amplifier:

Recall from the previous discussion that the Operational Amplifier can be configured to perform various and the operation that the Operational Amplifier performs is determined by the feedback network. Some of the commonly used and well known Operational Amplifier configurations are listed below:

Instrumentation Amplifier.

Buffer Amplifier.

Differential Amplifier.

Inverting Amplifier.

Non-Inverting Amplifier.

Transimpedance Amplifier.

Log Amplifier.

High Pass Filter.

Low Pass Filter.

Band Pass Filter.

Band-stop Filter and many more.

Non Inverting Summing Amplifier

I have discussed the general introduction of each of the above Operational Amplifier configurations in my previous post. Let us now understand the circuit for the Operational Amplifier based Summing Amplifier.
The circuit for the Operational Amplifier Summing Amplifier is shown in the figure below:

The circuit in the above image is basically the Inverting Summing Amplifier Operational Amplifier configuration. That is the Summing Amplifier configuration first adds the signals applied at the inverting input terminal and then inverts the sum at the output of the Operational Amplifier. It is important here to mention that the Operational Amplifier Summing Amplifier can also designed with the Non-Inverting configuration. The main difference between the Inverting and Non-Inverting Summing Amplifier configurations is the input impedance of each that is the input impedance of the Inverting Summing Amplifier configuration is comparatively less than the Non-Inverting Summing Amplifier configuration and this due to mainly to the feedback network. I will discuss the Non-Inverting Summer Amplifier in the next post and there I will discuss how the input impedance of the Operational Amplifier is affected by the feedback network. However in the signals to be added are applied at the Inverting input terminal in the above network and hence the linearity property of the Operational Amplifier is exploited. The signals are amplified according to the resistors through which they are fed to the Operational Amplifier and the sum of these amplified signals is inverted and appears at the Operational Amplifier.

Op amp Summing Amplifier:

Notice in the circuit diagram that the Operational Amplifier is used in the Inverting configuration that is the signals that are to be added are applied at the Inverting Input terminal. Also notice here the feedback network employed here as can be seen is purely resistive that is it consists of resistors only. The feedback network used in the above circuit for Summing Amplifier is actually the voltage divider network which acts to feed the portion of the output signal at the Inverting input terminal of the Operational Amplifier and thus in this way the feedback network controls the overall gain of the Summing Amplifier. It is important to mention here that the Operational Amplifier is categorized as the DC amplifier. This characteristic of Operational Amplifier of being the DC amplifier is very important in some applications and it means that the Operational Amplifier can amplify the DC signals at the input terminals in the same way as it amplifies the ac signals. So we can add the DC signals also in the Operational Amplifier based Summing Amplifier.

frequency response of amplifiers:

The AC analysis of the Operational Amplifier Summing Amplifier is shown in the figure below:

The input and output waveform form of the Operational Amplifier based Summing Amplifier is shown in the figure below :

The Simulation of the Summing Amplifier in Proteus is shown in the figure below:

As described earlier that the Operational Amplifier is the direct-coupled amplifier which means that the Operational Amplifier can amplify and manipulate the DC signals in the same way as it does for AC signals so the simulation of the Summing Amplifier for the DC signals is shown in the figure below;

That is all for now I hope this post would be helpful for you. In the next post I will come up with more interesting applications of the Operational Amplifier. Till then stay connected, keep reading and enjoy learning.

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Author: admin

I am Kashif Mirza, the founder of ProjectIOT123. I am an Embedded Engineer and working on Embedded Projects since 2003. I have worked on Arduino, Raspberry Pi, PIc Microcontroller, 8051 etc. and have designed both prototypes & industrial projects.